1. Field of the Invention
The present invention generally relates to equipment used for inspecting defects in semiconductor devices, and more particularly to a method and apparatus to observe and inspect coating defects in semiconductor wafers and to improve the quality of such coatings.
2. Description of the Related Art
Conventional spin-on coating processes are used in semiconductor manufacturing to deposit several layers on semiconductor substrates. Usually, a single-crystal silicon wafer is used in integrated circuit manufacturing. Additionally, spin-on coating processes are capable of being used in processes where the substrate to be coated does not exhibit a high degree of crystallinity.
Furthermore, coating materials applied by spin-coating processes include several types of materials such as 1) dopant containing materials which are subjected to post deposition treatment, such as heat treatment, to diffuse a dopant into a semiconductor substrate for forming, for example, a p-n diode junction therein; or 2) materials which, upon post-deposition treatment, form anti-reflective layers; or 3) electrically conductive materials for forming transparent or opaque electrodes or contacts; or 4) dielectric materials used as insulator layers, protective coatings, and gap-fill and damascene style metallization process materials; or 5) photoresist materials used in photolithographic or other types of selective patterning processing as by chemical or physical etching.
For example, a conventional spin-on coating technique of a dielectric material involves preparing a fluid consisting of the coating material dissolved, dispersed, or suspended in a suitable volatile solvent or other vehicle, along with any other process or product enhancing additive; dispensing an amount of the fluid on a substrate; i.e., a semiconductor wafer; and spinning the wafer with a rotational speed sufficient to spread the coating fluid in a uniform thickness over at least the portion of the wafer intended to be coated. The rotational speed, surface tension, and viscosity of the coating fluid generally determine the thickness of the resulting coating. Following spin-on deposition, the deposited film is cured at an elevated temperature and for a time sufficient to obtain a dielectric film having the desired properties.
Due to the submicron size of the devices involved and the speed of manufacturing, it is no surprise that defects arise in the spin-on coatings. However, the quality of the semiconductor substrate can vastly improve by detecting these defects, and curing them prior to further manufacturing, sale, and use of the device.
The evaluation of semiconductor wafer edges is a fundamental concern in quality control analysis in semiconductor manufacturing. The evaluation at the edge of the wafer is often times more critical to the production of high quality film coatings than other locations of the wafer because of the propensity of defects occurring near the edge of the wafer. These defects have many possible causes such as insufficient shot size, foreign material contamination, and non-uniform material build up. Most defect detection systems are not integrated with the deposition tool, especially spin-on deposition equipment because of the difficulty of maintaining a clear optical train between the wafer surface and the detector sensor.
High quality film coatings are a necessity to ensure a high quality semiconductor wafer and device. Many film coatings are applied by spin-on application techniques and often these coatings contain defects, and in order to remove the defects, a thorough defect detection system should be used. Poor quality coatings have a major impact on film quality, which in turn drives increased manufacturing costs due to the required rework necessary to achieve a high quality coating. Therefore, there is a need to improve the inspection capabilities of wafer detection systems in order to provide higher quality coatings, and an overall better quality semiconductor device.
In view of the foregoing and other problems, disadvantages, and drawbacks of the conventional wafer inspection and defect detection systems, the present invention has been devised, and it is an object of the present invention to provide an apparatus and method for detecting defects in semiconductor wafers by providing an inspection apparatus, which closely monitors the wafer including the edge region.
In order to attain the object suggested above, there is provided, according to one aspect of the invention a structure and method for improving a coating on a substrate, the structure comprising a chamber further comprising a holder, which holds the substrate; a supply of a coating material for coating the substrate in the chamber; a window in the wall of the chamber; and a supply of liquid for coating at least a portion of the window on the interior side of the chamber. The chamber is preferably adapted to house the window in multiple configurations. A camera, or other optical detector(s), which is positioned outside of the chamber, monitors the substrate through the window. Furthermore, the holder for the substrate rotates during the coating process.
In another aspect, the present invention encompasses methods using a wet window technique, wherein a flowing solvent in a laminar flow region is used to wet the surface and the optical window in order to intercept and remove contamination before it can impinge and stick to the optical window. If contaminants stick or attach to the optical window, they can obstruct the observation of the wafer, thus making the wafer quality determination difficult. The wet window does not introduce significant degradation of the optical signal because it is a substantially uniform film of liquid which gently flows over the window, much like adding on additional optical window only. This window is liquid rather than a typical solid window associated with conventional optical windows. The physical solid window acts as a uniform support for this liquid window.
The solid support window is preferably smooth enough that it does not introduce turbulence into the liquid flowing over the window, and it preferably does not have a significant solubility or chemical interaction with the liquid window.
The liquid window is preferably formed from a liquid that does not introduce a significant refraction that cannot be corrected by optical or electronic techniques; and the liquid is preferably a solvent for the contamination (resist, or other organic film spin-on the wafer), which would normally occlude the solid optical window, to a sufficient extent that this contamination would not build up and occlude or interfere significantly with the optical train.
In another aspect, the invention encompasses an apparatus and method involving the real-time defect detection feedback to avoid large amounts of product to be processed before the defect is observed and corrective action is taken. While the present technique is particularly suited for evaluation of the edge of a wafer, it can be applied to the total wafer as well, and thus maximize the percentage of defect corrected.